1. Field of the Invention
The present invention relates to an apparatus for vibration damping, and more particularly with respect to a viscous damper for space satellite applications.
2. Description of the Prior Art
A body moving in an oscillatory manner is said to be in vibration. Vibration is undesired in some systems because it may generate disturbing noise, cause errors in instrumentation mounted on the system, or, indeed, lead to physical destruction of the system if of sufficient amplitude. Thus, it is desirable to minimize the adverse effects of undesired vibrations. Vibration can be controlled by dissipating the vibratory energy. The resistance force that causes the vibration amplitude to decrease with time is called damping, and may be frictional or coulomb damping, which results when there is a sliding motion between two surfaces in contact, or viscous damping, where the magnitude of the damping force is directly proportional to the relative velocity between the two ends of a damping device. Viscous damping is desirable because it lends itself to linear, analytically predictive relationships, and the absence of coulomb-type friction assures no problems from wearout. Viscous damping may be represented by the sliding motion between lubricated surfaces or a component, such as a dashpot that is immersed in oil. Equations for the solution of damping parameters for viscous dampers are well known in the art. See, for example, C. M. Haberman, Vibration Analysis, Charles E. Merrill Pubs. Co., 1968.
Conventional vibration absorption devices consist typically of hydraulically damped springs or resilient elements interposed between a supporting structure and the equipment to be isolated from vibration. Damped springs in various forms and elastomeric pads are generally satisfactory for protecting equipment that is not sensitive to alignment. However, hydraulic devices generally require oil seals in the nature of resilient gaskets, which are subject to wear and leakage after extended use, while elastomeric or viscoelastic dampers may not retain structural alignment. Further, these devices may also introduce coulomb-type friction and are not generally useful for microinch displacements, and may have a damping coefficient which varies with displacement.
The present vibration absorption damper provides superior damping for displacements of the order of microinches. A hermetically sealed structure requires no sealing gaskets or other components subject to wear in operation. During vibration the damper yields axially and allows controlled damping of the structure to be isolated. Damping is independent of vibration amplitude or frequency over a wide range and relatively independent of temperature.
A disadvantage of prior art viscoelastic damping devices is that the damping coefficient may vary with the stiffness of the structure. Thus, distortion of the structure with an applied force results in a nonlinear damping response. The present invention provides a damping force which is directly proportional to velocity and independent of stiffness or displacement. An arch configuration provides substantial volumetric rigidity; that is, the structural deflection of the damping elements is directly proportional to the applied force. Relative to prior art dampers the present invention provides very large damping capability per unit weight or volume. In the form of a tubular assembly, the invention is particularly adapted to use as a damping support for structures or as one of a plurality of elements in a truss structure.